One of the important factors affecting design of an optical system (such as a system for an optical disk reader/writer, typically including a laser or other optical source, lenses, reflectors and other components) is the size of the optical system, both in terms of the mass, volume and/or dimensions and in terms of the size and shape of the light as it reaches the optical disk (the spot size and quality). Although a wide variety of systems have been used or proposed, typical previous systems have used optical components that were sufficiently large and/or massive that functions such as focus and/or tracking were performed by moving only some components of the system, such as moving the objective lens (e.g. for focus) relative to the laser or other light source. Without wishing to be bound by any theory, it is believed that the relatively large size of components was related to the spot size, which in turn was substantially dictated by designs in which the data layer of a disk was significantly spaced from the physical surface of the disk (so that the optical path typically passed through a disk substrate, or some other portion of the disk, typically passing through a substantial distance of the disk thickness, such as about 0.6 mm or more, before reaching the data layer).
Regardless of the cause behind providing for relative movement between optical components, such an approach, while perhaps useful for accommodating relatively larger or massive components, presents certain disadvantages, including the relatively large form factors required and the cost associated with establishing and maintaining optical alignment between components which must be made moveable with respect to one another. Such alignment often involves manual and/or individual alignment or adjustment procedures which can undesirably increase manufacturing or fabrication costs for a reader/writer, as well as contributing to costs of design, maintenance, repair and the like. Accordingly, it would be useful to provide an optical head method, system and apparatus which can reduce or eliminate the need for relative movement between optical components, during normal operation and/or can reduce or eliminate at least some alignment procedures, e.g., during reader/writer manufacturing.
Many early optical disks and other optical storage systems provided relatively large-format reader/writer devices including, for example, devices for use in connection with 12 inch (or larger) diameter disks. As optical storage technologies have developed, however, there has been an increasing attention to providing feasible and practical systems which are of relatively smaller size. For some applications, e.g., for use in personal electronic devices (PEDs), e.g. as described in U.S. patent application Ser. No. 09/315,398 for Removable Optical Storage Device and System (incorporated herein by reference), a device for reading and/or writing optical disks is described having a relatively small form factor such as about 10.5 mm height, 50 mm width and 40 mm depth. Generally, a practical reader/writer device must accommodate numerous items within its form factor including the media, media cartridge (if any), media spin motor, power supply and/or conditioning, signal processing, focus, tracking or other servo electronics, in addition to the components associated or affecting the laser or light beam optics. Accordingly, in order to facilitate a relatively small form-factor, it would be advantageous to provide an optical head apparatus, system and method which can occupy a relatively small volume. In addition to total volume considerations, constraints imposed by a desired form factor and/or the need to accommodate other reader/writer components can make it advantageous to provide an optical head apparatus system and method which is relatively small in certain dimensions such as having a relatively small vertical profile or dimensional requirement (with “vertical” referring to a direction parallel to the optical disk spin axis), although reduction of requirements in other dimensions (such as a longitudinal dimension parallel to an optical arm axis and/or a lateral dimension perpendicular to the longitudinal axis) may also be of importance. Provision of a low vertical profile configuration can be specially problematic since, for at least some optical designs (including, e.g. finite conjugate designs), a minimum optical path may be required or advisable (although the read/write beam generally must reach the optical disk substantially normal to the plane of the disk). Accordingly, it would be useful to provide an optical head apparatus system and method which can reduce dimensional requirements such as reducing vertical dimension requirements, e.g., in the case of a PED to less than about 12 mm, preferably less than about 5 mm and more preferably less than about 3 mm.
A number of optical reader/writer devices, including, for example, relatively large devices such as audio compact disk (CD) players in a typical home stereo system, present relatively little concern with power management or power budgets (typically having access to AC line level power or the like). As a result, in many such systems, it is feasible to provide an optical design which is relatively inefficient of optical power (such as by substantially overfilling lenses and the like, e.g. to accommodate noncircularity of laser sources). In contrast, devices such as those-described in this application Ser. Nos. 09/315,398, supra and or 60/140,633 intended to be lightweight and portable, generally must operate with a limited power budget (and also have a more limited ability to dissipate heat, compared with larger systems). Accordingly, it would be useful to provide a optical head apparatus system and method which can achieve the desired optical quality (e.g. accommodating noncircularity or other optical features) while avoiding undue energy inefficiency and/or unnecessary heat generation (e.g. arising from substantial overfilling of lenses or other optical inefficiencies which in turn require higher optical power and hence higher electrical power lasers which dissipate more heat).